1. Field of Invention
The present invention relates to a digital signal recording and reproducing device provided with an editor, and in particular, to a digital signal recording and reproducing device such as a digital video tape recorder which is provided with an editor for editing a digital video signal and is used for recording and reproducing a digital video signal coded at a high efficiency.
2. Description of the Related Art
In recent years, with the trend of improving the image quality and promoting digitization of video equipment, there have been put into practice recording and reproducing devices which utilize digital recording instead of the conventional analog recording. As a representative apparatus, a digital recording video tape recorder (referred to as a digital VTR hereinafter) has been put into practice. The digital VTR has such a feature that the digital VTR has a high image quality as compared with the conventional analog VTR and is substantially free from deterioration due to dubbing. However, the digital VTR has such a disadvantage that the amount of data to be recorded significantly increases when a digitized video signal is recorded as it is. Therefore, in order to enable a long-time recording using a compact cassette tape, it is required to introduce a high efficiency coding technique for reducing the amount of data of the video signal. As a digital VTR signal format using the high efficiency coding, for example, a digital VTR format having the specifications of Consumer-Use Digital VCRs using a 6.3 mm magnetic tape (referred to as a DV format hereinafter) has been proposed by HD Digital VCR Conference (High Definition Digital Video Cassette Recorder Conference). According to the format, a 4:2:2 component signal, which conforms to the component signal digital coding standard of the current television system provided in ITU-R BT. 601 of ITU Recommendation, is compressed to about 1/6.7 thereof by the high efficiency coding, thereby allowing a long-time recording to be achieved with a 1/4-inch width compact cassette tape.
When considering the replacement of the conventional analog VTR (referred to as an analog VTR hereinafter) with a digital VTR, the digital VTR is required to have functions equivalent to those of the analog VTR. In general, an editor for the recording and reproducing device such as a VTR or the like has two processing systems of:
a tape processing system for recording a video signal on a recording medium such as a magnetic tape or the like, thereafter processing data reproduced from the recording medium to convert the same reproduced data into a video signal, and outputting the video signal (referred to as a tape processing system hereinafter); and
an electric-to-electric processing system for outputting an inputted video signal as a video signal as it is (referred to as an EE processing system hereinafter). These two systems can be selectively switched according to a VTR mode.
During reproduction, the tape processing system is normally selected, and the data reproduced from the magnetic tape is processed to be converted into a video signal, and then, the video signal is outputted to a monitor television set. During recording, the EE processing system is selected since the user is required to simultaneously monitor the video signal of the data that is being recorded on the magnetic tape by means of the monitor television set. Further, in an insertion editing stage in which a further video image or sound is inserted in a magnetic tape that has been already recorded, these two modes are used in combination. That is, the EE processing system is selected for the interval for which the insertion recording is performed, and the tape processing system is selected for the other interval since it is required to output the video signal of the data that has been already recorded on the magnetic tape to the monitor television set. A method for implementing the EE processing system and the tape processing system will be described in detail below.
The prior art digital VTR provided with an editor is generally constructed as follows. An inputted video signal is converted into a digital signal by an analog-to-digital converter (referred to as an A/D converter hereinafter), and thereafter, the digital signal is compressed into video data having a predetermined amount of data by a high efficiency encoder. The compressed video data is processed by error correcting encoding, adding a parity for use in an error correcting process, and then, it is subjected to a modulation process for the recording thereof onto a magnetic tape, and the processed video data is recorded on the magnetic tape. When reproducing the video data recorded on the magnetic tape, the reproduced video data is inputted to a high efficiency encoder via a demodulation process and an error correcting decoding process. In the high efficiency encoder, the compressed video data is decompressed into the original video data, and thereafter, it is converted into an analog video signal by a digital-to-analog converter (referred to as a D/A converter hereinafter), then the analog signal is outputted.
In the above-mentioned prior art digital VTR, the processing system for processing the video data reproduced from the magnetic tape is the tape processing system. Further, in order to implement the EE processing system, it is required to output the video signal inputted to the digital VTR by putting the same video signal through a reproduction processing system for the magnetic tape in the middle of the processing. Therefore, the EE processing system is implemented by inputting the digital video data that has been converted by the A/D converter to the D/A converter after delaying the digital video data by a predetermined number of frames by means of a storage device. In the EE processing system, the video data is delayed using the storage device after the analog-to-digital conversion by the A/D converter. This is provided for the purpose of achieving a time coincidence between the video data to be recorded on the magnetic tape and the video data to be outputted to the monitor television set in the editing stage.
However, in the above-mentioned prior art digital VTR, there has been such a problem that the memory capacity of the storage device required for delaying the video data of the EE processing system for a timing matching of the video data of the EE processing system to the video data of the tape processing system (referred to as a timing matching hereinafter) becomes very large.
For example, in order to delay the 4:2:2 component signal by one frame, a memory of about 5.5 Mbits is required. Since a rearrangement process is executed in a unit of frame in the high efficiency encoding process and the high efficiency decoding process, and an intra-frame rearrangement process is executed in the error correcting encoding stage and the error correcting decoding stage when the above-mentioned DV format is used, then, a delay of a total of four frames occurs in the recording system and the reproduction system. Therefore, a storage device having a storage capacity of four frames=22 Mbits is required for the purpose of delaying the video data of the EE processing system obtained through the analog-to-digital conversion by the A/D converter.
For example, when the memory for the delaying of the EE processing system is removed for the purpose of reducing the circuit scale of the digital VTR, there occurs such a problem that the time correspondence relation between the output video signal to the monitor television set and the video data that is actually recorded on the magnetic tape is deviated in the editing stage. That is, the editing point confirmed on the monitor television set differs in time from the editing point on the magnetic tape in the editing process, and this may cause the user to erroneously perceive the editing point.